Various methods are being used as imaging technology that can obtain lengths in the depth direction of a subject as two-dimensional information (a range image) such as technology that uses a reference beam to measure the reflected light intensity and/or return time from the subject, stereoscopic ranging technology using multiple cameras, etc. Better subject recognition is possible by using range image information than by using the image information obtained from a normal camera. Therefore, the demand is increasing for applications of range image information as new input information in relatively inexpensive products for appliances, games, industrial applications, etc.
Among distance imaging methods, a solid state imaging device that includes an imaging optical system and multiple optical systems has been proposed as a configuration in which a single camera is used to obtain many sets of parallax and the ranging is performed based on triangulation. In such a solid state imaging device, multiple optical systems are disposed as a re-imaging optical system between the imaging optical system and the imaging element. For example, a microlens array in which many microlenses are formed on a plane is used as the multiple optical systems.
Multiple pixels are disposed under each of the microlenses. The images that are demagnified by the imaging optical systems are imaged on the imaging element by the microlens array. The simple-eye images that are imaged have viewpoints shifted by the amount of parallax existing due to the arrangement position of each microlens.
The distance estimation of the subject is possible using the principle of triangulation by performing signal processing of the images of the parallax image groups obtained from many microlenses. Further, it is possible to reconstruct the images as a two-dimensional image by performing image processing to link the images together.
In an imaging lens and a solid state imaging device, it is desirable to acquire both a high-precision range image and a good visible image.